1. Field of the Invention
The present invention relates to an optical information recording medium for recording information and reproducing the recorded information accomplished by application of a laser beam thereto, and more particularly to an optical information recording medium comprising a transparent substrate, a recording layer provided on the substrate, a reflection layer provided on the recording layer, and an anti-reflection layer provided on the back side of the substrate opposite to the recording layer, the anti-reflection layer comprising a plurality of overlaid layers, at least one of the layers being a transparent electroconductive layer.
2. Discussion of Background
Optical information recording media for recording information and reproducing the recorded information are widely known in the form of optical discs for movie films as well as optical audio discs, write-once type discs, and the like. Among these, an example of a magneto-optical recording disc on which rewriting is possible has been proposed in Japanese Patent Publication 62-27458. This magneto-optical recording disc comprises a recording layer composed of an amorphous rare earth element - transition metal alloy, such as TbFeCo or TbDyFeCo, sufficiently as thin as less than 400 .ANG. to transmit a laser beam, on which a reflecting layer is provided. A superior point of this structure is that it provides a reproduction signal with high intensity since both the Kerr effect and the Faraday effect can be utilized in this magneto-optical recording disc.
It can be said that the reproduction signal should be as intense as possible because the recording mark is minimized as the recording density and capacity are increased. Accordingly, a method of improving the reproduction characteristics has been proposed, as disclosed in Japanese Laid-Open Patent Application 59-79445, wherein an anti-reflection film layer is added to the above-mentioned structure, provided on the side of the substrate at which the laser beam enters, thereby reducing the reflection of the laser beam from the substrate surface as far as possible.
On the other hand, materials with high electrical resistance, for example, plastics such as polycarbonate resin and acrylic resin, and glass are used as the material for the substrate which supports a recording layer in an optical information recording medium. For this reason, there is usually a tendency for the optical information recording medium to become electrically charged. When the optical information recording medium becomes charged, minute particles of dust adhere to the outer surface of the medium because of static electricity. This hinders the write-in or read-out of the information, or causes malfunction of electronic circuits. With the object of preventing such an electric charge on the optical information recording medium, it has been proposed that a charge prevention layer be provided on the outer surface of the optical information recording medium (Japanese Laid-Open Patent Application 60-239946). It is desirable that the surface of the substrate of the optical information recording medium have the dual functions of preventing reflection and electric charging as outlined above, but an optical information recording medium provided with these two functions is not conventionally known.